Table 2.
Characteristics of the studies included in the systematic review
| Author | Technique | Study population | Results |
|---|---|---|---|
| Arda, 201120 | Shear wave elastography | 127 healthy volunteers (89 females, 38 males) with a mean age of 37.7 ± 9.11 years; range, 17–63 years) | The mean elasticity values were 10.4 ± 3.7 kPa for the masseter muscle. The same values in the longitudinal and transverse planes. Values in the longitudinal place were greater in males 10.8 ± 3.9 (range 4–20) than in females 10.3 ± 3.6 (range 2–23) with p value of 0.3. There was no correlation between age and elasticity of the muscle (p = 0.50). |
| Ariji, 200921 | Real-time sonographic elastography | 14 healthy volunteers (10 males and six females) and two female patients with TMD | The mean MSI of the right and left muscles in the healthy volunteers were 0.85 ± 0.44 and 0.74 ± 0.35. There was a significant correlation between the right and left MSI (R = 0.67, p < 0.001). The mean MSI was lower in males and in females (0.64 ± 0.34 and 1.05 ± 0.35; p = 0.008). MSI values of a 29-year-old female with TMD of the right masseter muscle were 2.06 for the right and 0.43 for the left masseter muscle. MSI values of a 46-year-old female with bilateral TMD were right 3.71 for the right and 0.22 for the left masseter muscle. |
| Ariji, 2012 | Strain sonoelastography | 35 healthy volunteers (20 males and 15 females) with a mean age of 41.4 ± 12.4 years; range, 25–65 years) | MEI was comparable for both masseter muscles with values of 0.79 ± 0.43 for the right side-and 0.74 ± 0.37 for the left side (p = 0.5737). A strong correlation was observed between the two sides (R = 0.7739; p < 0.001). |
| 8 TMD patients (2 males and six females) with unilateral myofascial pain with a mean age of 44.1 ± 9.6 years; range, 32–60 years) | MEI was higher for the symptomatic side-than for the contralateral side (1.13 ± 0.43 vs 0.77 ± 0.31; p = 0.03). The correlation between the two sides was insignificant (R = 0.4741; p = 0.2050). | ||
| Ariji, 201322 | Strain sonoelastography | ten healthy volunteers (8 males and two females) with a mean age of 40.9 ± 12.4 years; range, 26–54 years | MEI was comparable for both masseter muscles with values of 0.84 ± 0.21 for the right side-and 0.85 ± 0.21 for the left side. MEI increased significantly after exercise. |
| Ariji, 201623 | Strain sonoelastography | 37 TMD patients with myofascial pain (6 males and 31 females) with a median age of 45 years (range 9–83 years) | MEI was calculated at baseline and after 9.5 weeks of massage therapy. Patient were divided by response to the therapy. MEI in the therapy-effective was 1.33 at the baseline, 1.17 after the third treatment session, and 1.00 after the last treatment session. In the therapy-ineffective group, MEI were 1.20, 1.08, and 1.08, respectively. In the first group, values after the treatment were significantly lower in comparison to baseline, while in the second one, the differences were insignificant. |
| Ariji, 201623 | Strain and shear wave elastography | Phantoms and 30 healthy volunteers (21 males and nine females) with the median age of 31.5 years; range, 26–63 years | In healthy subjects, the average hardness on shear-wave sonoelastography was 42.82 ± 5.56 kPa at rest and 53.86 ± 8.26 kPa during jaw clenching. Differences between the left and right hardness values and between males and females were insignificant. |
| Badea, 201424 | Shear wave elastography | 25 healthy controls and 13 patients who had had radiotherapy for nasopharyngeal carcinoma (35 Gy minimum) | Shear waves velocities were measured in m/s. The values for relaxation and contraction in controls and patients presented no differences (1.79 ± 0.52 vs 1.72 ± 0.73; p = 0.72 and 1.70 ± 0.48 vs 1.59 ± 0.77; p = 0.98). Differences between groups were insignificant (1.79 ± 0.52 vs 1.65 ± 0.63; p = 0.78). |
| Damian, 2016 | Strain elastography | One case report of unilateral temporal myositis | Values not available. |
| Ewertsen, 201818 | Shear wave elastography | 10 healthy individuals (5 males and 5 females) with median age of 31 years and range from 22 to 46 years. | The mean shear wave speed in the parallel plane was 2.45 ± 0.25 m/s. The effect of sequence (day-to-day variation) and dominant side-were insignificant. The effect of scan plane in relation to muscle pennation was statistically significant. |
| Gotoh,2013 | Strain elastography | 10 healthy volunteers (8 males and 2 females) before, immediately after, and 10 min after static contraction | The EI ratios of the right and left masseter muscles were 0.84 ± 0.21 and 0.85 ± 0.21, respectively, before exercise, 1.75 ± 0.43 and 1.71 ± 0.43 immediately after exercise, and 0.90 ± 0.38 and 0.87 ± 0.36 10 min after exercise. There were no significant differences between the right and left EI ratios in any of the phases. The EI ratios immediately after exercise were significantly higher than those before exercise and 10 min after exercise on both right and left sides. |
| Herman, 201717 | Shear wave elastography | 176 volunteers with no known history of head and neck disease with a mean age of 48.8 years and range from 21 to 91 years. | The mean stiffness was 10.0 ± 4.3 kPa. A small increase with age was observed. BMI and weight had small effect on stiffness values. |
| Joy, 201525 | Shear wave elastography | 6 Thiel soft-embalmed human cadavers (3 males and 3 females) with a mean age at death of 81.3 ± 13.2 and range from 63 to 97 years. | Masseter 15.0 (95% CI: 6.3–35.5) kPa Sex, age at death and repeated measurements had no effect on elasticity. |
| Nakayama, 201526 | Strain elastography | Phantoms with elasticity of 20, 40 and 60 kPa. 25 healthy volunteers (10 females and 15 males) with a mean age of 30.8 ± 9.8 years and range from 20 to 53 years. |
No differences in EI ratios between males and females as well as between the right and left sides were observed. EI ration increased during clenching. Less variations were observed for the hard coupling agent. The EI ratios increased and showed wide variation with clenching. |
| Takashima, 201727 | Shear wave elastography | 26 females with bilateral masseter muscle pain who were classified as having TMD Ia (myofascial pain; n = 13) or Ib (myofascial pain with limited opening; n = 13) and healthy controls consisted of 24 females. Age range of TMD patients was 15 to 46 years, while controls 23–45 years. |
TMD Ia = 1.96 m/s (12.5 kPa) TMD Ib = 2.00 m/s (13.0 kPa) Healthy females = 1.27 m/s (5.25 kPa) Stiffness was significantly greater in TMD patients (p < 0.05). It was positively correlated with pain (p < 0.05) and negatively with maximum assisted mouth opening (p < 0.05) and painless mouth opening (p < 0.05). |
MEI, masseter muscle elasticity index calculated as the value of (the mean elasticity index of the masseter muscle)/(the mean elasticity index of the subcutaneous fat tissue) and was defined as the total hardness; MSI, masseter stiffness index defined as the ratio of elasticity of the fat tissues and elasticity of the masseter muscle; TMD, temporomandibular disorders; EI, elasticity index defined as the strain values of each area compared with the average strain value of the whole area of interest; EI ratio was calculated as the mean EI of scoring area divided by the mean EI of background.